Analysis of Rock Fracture Data from the Long Beach Oil Field

Fractures have significant control on the hydraulic behavior of reservoir fluids for petroleum wells. Fractures not only affect hydraulic conductivity, but also record the stress field at the time of their formation. Thus, fractures can be used to evaluate principal stress regimes. In this study, 10 electric borehole-image logs from oil exploration wells, located in the Long Beach Oil Field, were used to conduct a fracture analysis. The Long Beach Oil Field is located within the cities of Signal Hill and Long Beach, California, on the southwest margin of the Los Angeles basin. It is one of six major oil fields associated with the deformation of the Newport-Inglewood fault zone, which is a northwest-striking, dextral, strike-slip fault. By proximity, the Newport-Inglewood fault zone should be a significant stress producing structure relative to the Long Beach Oil Field. The wells used for this study vary in depth from 4,200 to 7,000 feet, and penetrate the Puente, Repetto, Pico, and San Pedro formations. Fractures were identified, cataloged and standardized among all the borehole-image logs. Fracture types were classified into six groups, which are: natural conductive fractures, natural resistive fractures, partial fractures, faults, induced fractures and borehole breakout. These fractures were examined using stereographic pole diagrams, rosette-strike plots, frequency diagrams and graphs. Fracture sets were interpreted and correlated based on fracture type, orientation, and relationship to lithology and formations. In-situ principal stress orientation of the study area was established from borehole breakout, and compared to data from the World stress map and local earthquake focal mechanisms in the literature. Principal stress orientations of natural fracture sets were interpreted using the Anderson stress model. These principal stress orientations are then compared to the interpreted in-situ stress established by the study from borehole breakout. Variations in principal stress orientations are interpreted as potential paleostress markers or localized principal stress changes due to structural changes. Furthermore, principal stress orientations obtained from the study are also compared to the predicted Riedel-shear model, applied locally to the Newport-Inglewood fault zone.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California